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  <title>检查给定的键名或索引是否存在于数组中</title>

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</div><hr /><div id="function.array-key-exists" class="refentry">
 <div class="refnamediv">
  <h1 class="refname">array_key_exists</h1>
  <p class="verinfo">(PHP 4 &gt;= 4.0.7, PHP 5)</p><p class="refpurpose"><span class="refname">array_key_exists</span> &mdash; <span class="dc-title">检查给定的键名或索引是否存在于数组中</span></p>

 </div>
 
 <div class="refsect1 description" id="refsect1-function.array-key-exists-description">
  <h3 class="title">说明</h3>
  <div class="methodsynopsis dc-description">
   <span class="type">bool</span> <span class="methodname"><strong>array_key_exists</strong></span>
    ( <span class="methodparam"><span class="type"><a href="language.pseudo-types.html#language.types.mixed" class="type mixed">mixed</a></span> <code class="parameter">$key</code></span>
   , <span class="methodparam"><span class="type">array</span> <code class="parameter">$search</code></span>
   )</div>

  <p class="para rdfs-comment">
   <span class="function"><strong>array_key_exists()</strong></span> 在给定的 <em><code class="parameter">key</code></em>
   存在于数组中时返回 <strong><code>TRUE</code></strong>。<em><code class="parameter">key</code></em>
   可以是任何能作为数组索引的值。<span class="function"><strong>array_key_exists()</strong></span>
   也可用于对象。
  </p>
   </div>

   
   <div class="refsect1 parameters" id="refsect1-function.array-key-exists-parameters">
    <h3 class="title">参数</h3>
    <p class="para">
     <dl>

      
       <dt>
<em><code class="parameter">key</code></em></dt>

       <dd>

        <p class="para">
         要检查的键。
        </p>
       </dd>

      
      
       <dt>
<em><code class="parameter">search</code></em></dt>

       <dd>

        <p class="para">
         一个数组，包含待检查的键。
        </p>
       </dd>

      
     </dl>

    </p>
   </div>
    
   
   <div class="refsect1 returnvalues" id="refsect1-function.array-key-exists-returnvalues">
    <h3 class="title">返回值</h3>
    <p class="para">
     成功时返回 <strong><code>TRUE</code></strong>， 或者在失败时返回 <strong><code>FALSE</code></strong>。
    </p>
   </div>

   
   <div class="refsect1 examples" id="refsect1-function.array-key-exists-examples">
    <h3 class="title">范例</h3>
    <p class="para">
     <div class="example" id="example-4855">
      <p><strong>Example #1 <span class="function"><strong>array_key_exists()</strong></span> 例子</strong></p>
      <div class="example-contents">
<div class="phpcode"><code><span style="color: #000000">
<span style="color: #0000BB">&lt;?php<br />$search_array&nbsp;</span><span style="color: #007700">=&nbsp;array(</span><span style="color: #DD0000">'first'&nbsp;</span><span style="color: #007700">=&gt;&nbsp;</span><span style="color: #0000BB">1</span><span style="color: #007700">,&nbsp;</span><span style="color: #DD0000">'second'&nbsp;</span><span style="color: #007700">=&gt;&nbsp;</span><span style="color: #0000BB">4</span><span style="color: #007700">);<br />if&nbsp;(</span><span style="color: #0000BB">array_key_exists</span><span style="color: #007700">(</span><span style="color: #DD0000">'first'</span><span style="color: #007700">,&nbsp;</span><span style="color: #0000BB">$search_array</span><span style="color: #007700">))&nbsp;{<br />&nbsp;&nbsp;&nbsp;&nbsp;echo&nbsp;</span><span style="color: #DD0000">"The&nbsp;'first'&nbsp;element&nbsp;is&nbsp;in&nbsp;the&nbsp;array"</span><span style="color: #007700">;<br />}<br /></span><span style="color: #0000BB">?&gt;</span>
</span>
</code></div>
    </div>

   </div>
     </p>
     <div class="example" id="example-4856">
      <p><strong>Example #2 <span class="function"><strong>array_key_exists()</strong></span> 与 <span class="function"><a href="function.isset.html" class="function">isset()</a></span> 的对比</strong></p>
      <div class="example-contents"><p>
       <span class="function"><a href="function.isset.html" class="function">isset()</a></span> 对于数组中为 <strong><code>NULL</code></strong>
       的值不会返回 <strong><code>TRUE</code></strong>，而
       <span class="function"><strong>array_key_exists()</strong></span> 会。
      </p></div>
      <div class="example-contents">
<div class="phpcode"><code><span style="color: #000000">
<span style="color: #0000BB">&lt;?php<br />$search_array&nbsp;</span><span style="color: #007700">=&nbsp;array(</span><span style="color: #DD0000">'first'&nbsp;</span><span style="color: #007700">=&gt;&nbsp;</span><span style="color: #0000BB">null</span><span style="color: #007700">,&nbsp;</span><span style="color: #DD0000">'second'&nbsp;</span><span style="color: #007700">=&gt;&nbsp;</span><span style="color: #0000BB">4</span><span style="color: #007700">);<br /><br /></span><span style="color: #FF8000">//&nbsp;returns&nbsp;false<br /></span><span style="color: #007700">isset(</span><span style="color: #0000BB">$search_array</span><span style="color: #007700">[</span><span style="color: #DD0000">'first'</span><span style="color: #007700">]);<br /><br /></span><span style="color: #FF8000">//&nbsp;returns&nbsp;true<br /></span><span style="color: #0000BB">array_key_exists</span><span style="color: #007700">(</span><span style="color: #DD0000">'first'</span><span style="color: #007700">,&nbsp;</span><span style="color: #0000BB">$search_array</span><span style="color: #007700">);<br /></span><span style="color: #0000BB">?&gt;</span>
</span>
</code></div>
   </div>

     </div>
   </div>

   
   <div class="refsect1 notes" id="refsect1-function.array-key-exists-notes">
    <h3 class="title">注释</h3>
    <blockquote class="note"><p><strong class="note">Note</strong>: 
     <p class="para">
      为了向下兼容，可以使用下列已废弃的别名：
      <span class="function"><a href="function.key-exists.html" class="function">key_exists()</a></span>
     </p>
    </p></blockquote>
    <blockquote class="note"><p><strong class="note">Note</strong>: 
     <p class="para">
      For backward compatibility reasons, <span class="function"><strong>array_key_exists()</strong></span>
      will also return <strong><code>TRUE</code></strong> if <em><code class="parameter">key</code></em> is a property
      defined within an <span class="type"><a href="language.types.object.html" class="type object">object</a></span> given as
      <em><code class="parameter">search</code></em>. This behaviour should not be relied upon,
      and care should be taken to ensure that <em><code class="parameter">search</code></em> is
      an <span class="type"><a href="language.types.array.html" class="type array">array</a></span>.
     </p>
     <p class="para">
      To check whether a property exists in an object, use
      <span class="function"><a href="function.property-exists.html" class="function">property_exists()</a></span>.
     </p>
    </p></blockquote>
   </div>

   
   <div class="refsect1 seealso" id="refsect1-function.array-key-exists-seealso">
    <h3 class="title">参见</h3>
    <p class="para">
     <ul class="simplelist">
      <li class="member"><span class="function"><a href="function.isset.html" class="function" rel="rdfs-seeAlso">isset()</a> - 检测变量是否设置</span></li>
      <li class="member"><span class="function"><a href="function.array-keys.html" class="function" rel="rdfs-seeAlso">array_keys()</a> - 返回数组中所有的键名</span></li>
      <li class="member"><span class="function"><a href="function.in-array.html" class="function" rel="rdfs-seeAlso">in_array()</a> - 检查数组中是否存在某个值</span></li>
      <li class="member"><span class="function"><a href="function.property-exists.html" class="function" rel="rdfs-seeAlso">property_exists()</a> - 检查对象或类是否具有该属性</span></li>
     </ul>
    </p>
   </div>

   
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